1. Field of the Invention
The present invention is generally related to a method for preventing fouling of a submerged surface and, more particularly, to a method for improving the effectiveness of a fouling prevention system while also avoiding the destruction of conductive materials used in conjunction with those submerged surfaces.
2. Description of the Related Art
Biofouling of submerged surfaces is a serious problem, particularly with regard to the hulls of boats used in saltwater environments. Those skilled in the art of marine vessels and propulsion systems have been addressing this problem for over 100 years. Some of the patents cited by the patents described immediately below were granted prior to 1914. Those patents and many more are described in the patents cited immediately below and are generally familiar to those skilled in the art. Prior attempts to prevent or discourage biofouling of submerged surfaces have used chemical treatments on those surfaces, various gases bubbled below and onto those surfaces, and various electrical schemes to generate noxious gases which inhibit or discourage the growth of marine organisms on submerged surfaces.
U.S. Pat. No. 6,173,669, which issued to Staerzl on Jan. 16, 2001, disposes an apparatus and method for inhibiting fouling of an underwater surface. The system comprises two conductive surfaces and a device that alternates the direction of electric current between the two surfaces. The current is caused to flow through sea water in which the two surfaces are submerged or partially submerged. A monitor measures the current flowing from one of the two conductive surfaces and compares it to the current flowing into the other conductive surface to assure that no leakage of current of substantial quantity exists.
U.S. Pat. No. 6,209,472, which issued to Staerzl on Apr. 3, 2001, discloses an apparatus and method for inhibiting fouling of an underwater surface. The system provides an electric current generator which causes an electric current to flow proximate the underwater surface. A source of power, such as a battery, provides electrical power to the electric current generator. The flow of current passes from the underwater surface to water surrounding the surface or in contact with the surface, and a point of ground potential. The point of ground potential can be a marine propulsion system attached to a boat on which the underwater surface is contained.
U.S. Pat. No. 6,547,952, which issued to Staerzl on Apr. 15, 2003, discloses a system for inhibiting fouling of an underwater surface. An electrically conductive surface is combined with a protective surface of glass in order to provide an anode from which electrons can be transferred to seawater for the purpose of generating gaseous chlorine on the surface to be protected. Ambient temperature cure glass (ATC glass) provides a covalent bond on an electrically conductive surface, such as nickel-bearing paint.
U.S. Pat. No. 6,973,890, which issued to Staerzl on Dec. 13, 2005, discloses a self-adaptive system for an apparatus which inhibits fouling of an underwater surface. The system automatically calibrates a marine fouling prevention system. It responds to movements between fresh and saltwater bodies of water, detects damage to the hull or other submerged surface, and responds to the use of the fouling prevention system with different sizes of marine vessels.
U.S. Pat. No. 7,025,013, which issued to Staerzl et al. on Apr. 11, 2006, discloses a multilayered submersible structure with fouling inhibiting characteristics. The structure has an outer coating that is disposed in contact with water in which the structure is submerged, a current distribution layer or charge distribution layer, an electrical conductor connectable in electrical communication to a source of electrical power, and a support structure.
U.S. Pat. No. 7,131,877, which issued to Staerzl on Nov. 7, 2006, discloses a method for protecting a marine propulsion system. An electrical conductive coating is provided on a housing structure of a marine propulsion system. By impressing a current on the electrically conductive coating, which can be a polymer material, the housing structure is used as an anode in a cathodic protection system. In addition, the use of the electrically conductive coating on the housing structure of an anode inhibits the growth of marine fouling on the outer surface of the housing structure by forming chlorine gas in a saltwater environment and by forming an acidic water layer near the surface in a non-saltwater environment.
U.S. Pat. No. 7,211,173, which issued to Staerzl et al. on May 1, 2007, discloses an improved system for inhibiting fouling of an underwater surface. The system comprises first and second conductors which are made of a polymer matrix, such as vinyl ester, and a suspended conductor, such as graphite powder or particles.
U.S. patent application Ser. No. 10/794,166 (M09775), which was filed by Staerzl on Mar. 5, 2004, discloses a method for discouraging growth of organisms in a non-saltwater environment. The method changes the chemical characteristics, ionic species, or the pH of a liquid immediately proximate a first surface. This creates an environment in that specific region which is anathema to marine organisms such as algae. It discourages the growth of marine organisms by changing the characteristic, such as the pH, of the non-saltwater liquid, to make it more acidic and less habitable to the marine organisms.
The patents described above are hereby expressly incorporated by reference in the description of the present invention.
It has been discovered that certain conductive materials are subject to destructive results when electric current is passed through the conductive surfaces while they are submerged. Although chlorine gases are produced at these conductive surfaces as a result of the current flowing through them, the conductive material can be oxidized as a result. For example, if carbon particles are used to provide the conductive surface, the carbon can be oxidized to carbon monoxide or carbon dioxide gas. As this occurs, the carbon is eventually dissipated and the effectiveness of the conductive surface is deleteriously affected. Eventually, the conductive surface becomes completely ineffective and must be repaired or replaced. It would therefore be significantly beneficial if a method could be provided which allowed for a proficient production of chlorine gas at the conductive surface in salt water and a pH change in fresh water, but avoided the destruction of the conductive material by an oxidation process.